Skellige festive slippers are light armor footwear in The Witcher 3: Wild Hunt, which can be found in Yennefer's room at The New Port inn at Kaer Trolde Harbor. They are also sold by Elihal, Sjusta and the Kaer Trolde citadel armorer.
Yennefer recommends Geralt to wear them in 1272 when they both attended a banquet honoring King Bran's death. She also recommends he wear Skellige breeches and an Elegant Skellige shirt.